Physics - Verification

posted by .

Hello, just wanted to verify is what I did is good. I posted this question yesterday and Bob helped me, so just wanted to be sure it's good.

The problem is:

A bloc of 10 kg is put at the top of an inclined plan of 45 degrees (to the left), attached to a spring which has a spring constant of 250 N/m. The coefficient of kinetic friction between the bloc and the surface of the inclined plan is of 0,300.

What is the maximum elongation of the spring?

First I went to find fc :

EFy = 0
n - mg*sinTHETA
n = mg*sinTHETA*mu
n = 10kg*9.8N/kg*sin45*0.300
n = 20.8 N

then I know that Us = 1/2kx^2
and that Ug = mgycosTHETA*x


Ef = Kf + Ugf

Ef = 1/2kx^2 + mg*cosTHETA*x

Ef = 125x^2 + 29.4x

Ef = Ei + Wnc <-- My friction force


125x^2 - 29.4x = 0 - 20.8x
125 x^2 = 8.6x
125x = 8.6
x = 0.0688 meters or 6.8 cm.

does that make sense?

Thank you!

  • Physics - Verification -

    made a mistake when I wrote Ef = Kf + Ugf

    instead it's -->

    Ef = Kf + Ugf + Usf

  • Physics - Verification -

    where Kf is = 0

  • Physics - Verification -

    No it does not make sense.

    Workdone by gravity= force down plane*distance= mg*sinTheta*x

    Work done on spring: 1/2 k x^2

    Work done on friction: mg*cosTheta*mu*x

    mgSinTheta*x=1/2 kx^2+mgCosTheta*mu*x

    divide by x, then group terms

    1/2 kx=mg(SinTheta-mu*CosTheta)


    x=98/125 *.7*.7= .392m

    check my thinking.

  • Physics - Verification -

    ohhh I see now, but when you say Work done on spring, you take the Energy formula which is 1/2 k x^2 , wouldn't the work on a spring be mu*N*x?

  • Physics - Verification -

    and why isn't it Wg = Wspring - Wfriction

    as friction is going to other way?

  • Physics - Verification -

    nevermind my first question, my mistake hehe

  • Physics - Verification -

    your second quesion. Friction absorbs energy, as does the spring. They add to equal the energy input of the system.

  • Physics - Verification -

    okay cool, thanks a lot Bob

Respond to this Question

First Name
School Subject
Your Answer

Similar Questions

  1. grammar

    Ms.writeacher, I'm sorry i was just trying to ask to verify in the grammar if that was what you were referring to. My apologies to you. thank you for your responce . No problem. I just wanted to make sure you found my other responses. …
  2. physics-bobpursley/drwls

    Good morning! I just wanted to say thank you for all of your help. This was my first time taking Physics ever and it was like a foreign language to me. For a long time during this semester I had an "F" average, because of you both …
  3. Jiskha

    Good evening everyone, I just wanted to know why people on this computer keep getting blocked from this site...I tried to ask and answer questions a couple of days ago and was unable to because I was obviously blocked. Whenever i pressed …
  4. college courses

    Good Morning All! so yesterday i posted something about college that i wanted to know. well, i'm at Georgia State right now. i said i wanted to do something in the designing field. i think that's fine because they have a college of …
  5. science

    I was just wondering! I posted a question for you all at 12:01 today. Are you allowed to help me with this type of question?
  6. Just Curious

    Hey. I was just wondering if anybody on here has been to teenink. I can't post the website but if you Google teen ink, it takes you to it. It is a very interesting site for teenage writers. I just wanted to let people who might be …
  7. Calculus - Verification

    Hello, I just wanted to verify this definite integral and if my answer is good: a = 1 and b = 4 integral of (1 - 1/x^2)(x^2 + 1/x) dx = (x + 1/x)(x^3/3 + lnx) + C (4 + 1/4)(64/3 + ln4) - (1 + 1)(1/3 + ln1) = 96.56 - 0.6666 = 95.89 …
  8. Please Read

    I just wanted to say thanks to all of the teachers who help out the kids on here because without you guys we do not know where we would be. You guys take out the time of your day to help us out and I really appreciate it and I'm sure …
  9. English

    I scored 3428 on my scantron test. Is that a good score?
  10. message for Dr. BOB

    Dear Dr. Bob, I just wanted to thank you. You helped me graduate from college by helping me with with chemistry and now I am getting my master's degree. You have no idea what you have done for me. Again, THANK YOU!

More Similar Questions